Synthetic-resin bags which are open at one end are available in stacks and are adapted to be filled with condiments, comestibles or other materials in automatic filling machines. For such machines to be effective, it is necessary to de-stack the bag, i.e., remove the individual bag from a stack thereof in a magazine, and to open the bag to permit the filling thereof.
The filling machine may be provided with a transfer chain onto which the open bags are fed for transport to the filling device.
The bags of interest for the purposes of the present invention are those which are composed of a relatively flexible synthetic resin thermoplastic which is thermally sealable and which comprises two substantially rectangular walls connected by rectilinear thermal seams or welds on three sides while the fourth side remains unseamed or unsealed, to permit its opening for filling.
Such bags are commercially available under the name "DOYPACK" and have two lateral walls which are substantially rectangular and are provided at the bottom with gussets or weld seams generally having a bottom of W-section pattern so that the lateral walls can be spread apart to permit the bag to be self-standing (see U.S. Pat. Nos. 3,380,646, 3,637,133 and 3,935,993).
The known processes for opening such bags include the following:
In a first system which has been used commercially, the bags are withdrawn from a magazine or supply in which they are stored flat by a member provided with suction heads. The suction heads are evacuated to attract the flat bag from the magazine. The bags on this member are then introduced between pincers of a support mounted on the transfer chain. At a downstream location or station, the mouth of the bag is opened by means of inclined planes provided with suction devices between which the mouth of the bag is passed. Full opening of the bag is effected by blowing through the open mouth with compressed air at low pressure.
In certain other machines, the opening system consists of means for opening the upper lips of the bag by suction and then introducing into the bag a mechanical element which effects the unfolding of the bottom of the bag and hence complete opening thereof.
The two systems have been found to have practical drawbacks of considerable significance:
In the case of the first system, it is found that if the bag is difficult to open, a significant overpressure develops within the bag. The spreading of the bottom is thus effected suddenly which produces a shock wave capable of destroying or damaging the bag. Furthermore, with certain types of bags, opening does not occur by inflation and in such machines, there is a significant percentage of non-opened bags.
In the second case, the introduction of a mechanical member into the fragile bag also is capable of damaging the film from which it is made. Furthermore, the introduction of a mechanical element to some depth within the bag which is to be subjected to a horizontal displacement (translation) reduces sharply the cadence at which the machine can operate and creates the supplemental risk that the two mutually perpendicular movements will interfere with one another.
Finally, in both cases it is necessary to provide, on the transfer chain, a special space for carrying out this opening of the bags or sacks which, depending upon the size of this space, results in an increase in the size of the machine and the space occupied thereby.
It should be noted further that there are known devices which comprise movable members carrying suction heads which are capable of drawing the bags or sacks from the magazine and then opening them. These devices, however, have been highly complex heretofore and generally require three members movable in translation as well as two members which describe a rotating movement. In other words, such systems have the same inconveniences as the other systems described previously with respect to the possible interference of different types of movements, complexity and synchronization because they also effect a withdrawal of the bag from the magazine at a first location and an opening of the bag at a second location spaced from and distinct from the first. The requirement that two separate stations be provided is, of course, a significant disadvantage.